been syndactylous, and the authors of the account[[85]] of these bones think that the fourth toe may have shared in this syndactyly. The metatarsal of the fifth digit is enormously expanded at its edge, and seems to have furnished a strong support to the creature; this is also seen in the metacarpal of the fore-limb. Probably, therefore, Diprotodon was quadrupedal in its mode of progression, with the emphasis laid upon the little finger and the little toe instead of, as in ourselves, the first toe. The hind-foot of the Diprotodon could not be more unlike that of a Kangaroo than it actually is.

Fig. 73.—Diprotodon australis. (After Owen.) Fig. 74.—Thylacoleo carnifex. Side view of skull. (After Flower.)

Another giant among these Marsupials was the genus Thylacoleo, whose name was given to it by Sir Richard Owen on the view that it was a Marsupial Tiger. Sir W. Flower has, however, controverted this opinion, and the genus is in fact, in spite of its large size, closely allied to the Phalangers and

Cuscuses.[[86]] The dental formula is I 3/1 C 1/0 Pm 3/1 M 1/2; the last premolar is a great blade-shaped tooth like that of Potorous.

Nototherium was a creature smaller than Diprotodon, but still of large size; it is believed to have been a burrowing creature, and to connect the Wombats with Diprotodon. More certainly allied to the existing Wombat was Phascolonus, a Wombat as big as a Tapir.

Fig. 75.—Nototherium mitchelli. Side view of skull. × 1⁄6. (After Owen.)

Of extinct American Diprotodonts the Epanorthidae, already referred to in connexion with the living Caenolestes, were the most prominent forms. The genus Epanorthus occurs in the Santa Cruz formation of Patagonia, which is believed to be Miocene. The incisors are three in the upper jaw; and the single incisor of each ramus of the lower jaw is a great chisel-shaped, cutting instrument.

Abderites is also typically Diprotodont by reason of the large projecting incisors of the lower jaw. It has a large cutting tooth in the lower jaw, which appears to be the last premolar, and is thus comparable to the great cutting tooth of the lower jaw and of the upper jaw of the extinct Phalanger, Thylacoleo.

It may also be comparable to the great premolar of such Multituberculata as Ptilodus and Plagiaulax. It is, moreover, marked with vertical grooves.